1. Field of the Invention
This invention relates to magnetic recording media in the form of tapes or disks for various purposes and more particularly, to an improvement in a magnetic recording layer of the media of the type mentioned above.
2. Description of the Prior Art
Most magnetic powders used in a magnetic recording layer of, for example, a video tape are acicular magnetic powders. The acicular magnetic powder is oriented in the magnetic recording layer along the length of a base film. When, however, the magnetic tape is used for recording a signal of a short wavelength, there is the disadvantage that the reproduction output lowers because of the large self-demagnetizing effect of the tape. A recording signal of a shorter wavelength generally results in a larger self-demagnetizing effect, thus leading to a lower reproduction output. Accordingly, this type of magnetic tape cannot be adapted for high density recording.
Another type of magnetic tape has been proposed in which a magnetic ferrite powder of a hexagonal system is used so that the c axis of the ferrite powder is oriented vertically with respect to the surface of a base film. This magnetic tape involves little problem on the self-demagnetization in a short wavelength region, but will bring about a lowering of reproduction output when a ring-type magnetic transducer head is used for recording and reproduction operations. This is because the magnetic field generated from the head along the lengthwise direction cannot be sufficiently utilized. Especially, in a long wavelength region where the magnetization for recording is predominantly composed of a lengthwise component, the reproduction output lowers considerably.
In order to utilize the merits of both types of magnetic tapes set forth above, attempts have been made to fabricate magnetic recording media which employ both an acicular magnetic powder and a magnetic ferrite powder of a hexagonal system.
Although the acicular magnetic powder and the magnetic ferrite powder are both magnetic in nature, their characteristics are significantly different from each other. For instance, the magnetic ferrite powder has very poor dispersability in liquid mediums. Especially, when carbon black is added as a conductive material for antistatic purposes in a magnetic recording layer, the dispersability becomes poorer. Presumably, this results from the synergistic effect of carbon black and the ferrite powder of a hexagonal system.
In order to improve the dispersability, attempts have been made to use a magnetic ferrite powder whose plate ratio is relatively small because such a powder is considered to be more dispersable. It has been also attempted to reduce the amount of the magnetic ferrite powder. However, these attempts are not satisfactory because the merits of the magnetic ferrite powder are, more or less, sacrificed.